fix(verifier): use reachable solc list mirror and persist compilers

[vriveraPeersyst]

Why

The smart-contract-verifier could not verify contracts (error: Couldn't fetch the file … https://solc-…). From inside the container it failed to fetch the Solidity compiler list from https://binaries.soliditylang.org/linux-amd64/list.json. Without that catalog the service cannot resolve/download the requested compiler (e.g. 0.8.30), so verification fails.

⚠️ Root cause not fully confirmed from the container. The fetch fails, but the exact cause (egress firewall vs. DNS vs. server-side 403/429 vs. Cloudflare blocking datacenter IPs / non-browser clients) has not been read from the container logs yet. See How to confirm below. This PR is the repo-level remedy for the most likely causes; if the container has no GitHub egress either, the fix must be at the network layer.

What

1. Repoint the Solidity LIST_URL to the canonical GitHub mirror — https://raw.githubusercontent.com/ethereum/solc-bin/gh-pages/linux-amd64/list.json. Same content binaries.soliditylang.org is served from, confirmed current (contains 0.8.30). Original soliditylang URL kept as a commented fallback with a WHY note. The blockscout/solc-bin mirror was rejected — stale (max 0.8.14).
2. Persist the compiler caches — bind-mount volumes for /tmp/solidity-compilers and /tmp/vyper-compilers (matching the existing stats-db-data / redis-data convention) so downloaded compilers survive container restarts.
3. gitignore the two new data dirs.

Files: docker-compose/envs/common-smart-contract-verifier.env, docker-compose/services/smart-contract-verifier.yml, .gitignore.

How to confirm the root cause (from the Docker host)

docker logs smart-contract-verifier 2>&1 | grep -i -A3 'list\|fetch\|solc'
docker exec smart-contract-verifier sh -c \
  'wget -S -O /dev/null https://binaries.soliditylang.org/linux-amd64/list.json'
#   timeout            -> egress blocked
#   403/429            -> server/Cloudflare refusing (datacenter IP / non-browser client)
#   could not resolve  -> DNS
#   200 OK             -> URL works; cause is elsewhere (this PR would not be the fix)

How to test

1. Deploy with these env/compose changes.
2. From the container, confirm it reaches the new mirror: docker exec smart-contract-verifier sh -c 'wget -S -O /dev/null https://raw.githubusercontent.com/ethereum/solc-bin/gh-pages/linux-amd64/list.json' → expect 200 OK.
3. Verify a contract compiled with 0.8.30 / cancun; should succeed.
4. Restart the container and re-verify — compiler should already be cached.

Notes

• docker unavailable in the dev environment; changes validated by inspection. Runtime test-verify is the deployment step above.
• Upstream blockscout/blockscout ships these two files identically — no upstream fix to port; the default assumes the container has egress to soliditylang.

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